Fotokol - A snapshot of developments since Chad in mid-January sent troops to Cameroon, culminating on Tuesday in it sending ground troops into Nigeria for the first time to fight Boko Haram Islamists.
Boko Haram, which has in the last six months seized dozens of towns and villages across the country, in January launched a full-scale assault on Baga, which straddles the borders of Chad, Nigeria, Niger and Cameroon.
-- JANUARY 2015 --
- 16: Dozens of Chadian tanks head south towards Cameroon to help fight Boko Haram, after N'Djamena's parliament votes to send armed forces to Cameroon and Nigeria, whose army has been heavily criticised for failing in its fight against the Islamists.
On January 14, Chad's government had pledged "active support" for Cameroon in fighting Boko Haram, after another cross-border raid by the insurgents.
Also read: Boko Haram threat could pose 'regional crisis': US
- 17: A huge convoy of some 400 Chadian vehicles arrives in the Cameroon border town of Kousseri. Chad's president, who accompanies his troops to the frontier, calls on countries in the region to form a "large coalition" against Boko Haram.
- 30-31: The African Union calls at a summit in Addis Ababa for a regional five-nation force of 7,500 troops to defeat the rise of Boko Haram, saying its brutality "requires a collective, effective and decisive response".
- 31: Chadian aircraft bomb the Nigerian town of Gamboru along with the Cameroon border in an operation targetting Boko Haram.
-- FEBRUARY --
- 2: A blast rips through a car park outside a stadium where Nigeria's President Goodluck Jonathan has just addressed a re-election campaign rally in the northeastern city of Gombe.
The attack has not been claimed, but two female suicide bombers are suspected of being behind the blast.
- Military claims it has retaken Gamboru and four other towns held by Boko Haram following a joint weekend offensive by its military, civilian vigilantes and forces from Chad and Cameroon.
- 3: Chad sends ground troops into the country for the first time, with its warplanes striking Boko Haram positions, followed by armoured vehicles rolling across the bridge linking Fotokol town in Cameroon with Gamboru in Nigeria, clearing the way for the infantry who seize Gamboru, according to an AFP reporter.
Chadian forces are also deployed near two villages in Niger just across the border from Nigeria.
Nigeria's military says the country's sovereignty is not compromised despite the presence of Chadian ground troops.